Thread break sensing device for sewing machines



April 17, 1962 I E. P. TURNER ETAL 3,029,763

THREAD BREAK SENSING DEVICE FOR SEWING MACHINES Filed Aug. 3, 1959 2Sheets-Sheet 1 IN VEN TOR. Edgar P. Turner and BY A/ber/ /V. 600kTTORNEY April 17, 1962 E. P. TURNER ETAL 3,029,763

THREAD BREAK SENSING DEVICE FOR SEWING MACHINES 2 Sheets-Sheet 2 FiledAug. 3, 1959 INVENTOR. Edgar P. Turner and B Albert M Cook TTORWY UnitedEdgar P. Turner, Watchung, and Albert N. Cook, Rernardsville, Ni,assignors to The Singer Manufacturing Company, Elizabeth, N.J., acorporation of New Jersey Filed Aug. 3, 1959, Ser. No. 831,299 Claims.(Cl. 112-419) The present invention relates to a device for sensing andresponding to a break in or exhaustion of the supply of the thread in asewing machine.

Prior thread break sensing devices have been objectionable in that theyrequired a sensing device in continuous contact with and placing a dragon the thread at all times during the stitching cycle. It is desirableat certain times in the stitch forming cycle that a minimum of tensionor drag be placed on the thread. Prior devices have not met thisrequirement.

An object of this invention is to provide a sensing device which placesdrag on the thread during that portion only of the stitching cycle atwhich it will not affect proper stitch formation.

It is a further object of this invention to provide a single sensingdevice to detect breakage or e" raustion of the supply of either theneedle thread or the bobbin thread.

The aforementioned objects are accomplished by the present inventionwhich is so arranged as to apply a drag on the thread in that portiononly of the sewin cycle when the already formed stitch is being set andthread is being drawn from the thread supply. These two actions occur asthe take-up arm approaches the top of its stroke. During this portion ofthe sewing cycle the thread is drawn tight by the take-up and additionaldrag does not adversely affect stitch formation.

Having in mind the above and other objects that will be evident from anunderstanding of this disclosure, the invention comprises the devices,combinations and arrangements of parts as illustrated in the presentlypreferred embodiment of the invention which is hereinafter set forth insuch detail as to enable those skilled in the art readily to understandthe function, operation and advantages of it when read in conjunctionwith the accompanying drawings in which:

FIG. 1 is a side elevational view of the head portion of a sewingmachine bracket arm having the present thread "break sensing deviceapplied thereto.

FIG. 2 is a front elevational view of the sewing machine face plate. a

FIG. 3 is a fragmentary top view of the bracket arm head showing theposition of the thread break sensing member relative to the take-up armwhen the thread is unbroken.

FIG. 4 is a view similar to FIG. 3, but showing the position of thethread break sensing member when the thread is broken or the threadsupply is exhausted.

FIG. 5 is an enlarged side elevational view of the bracket arm head ofthe machine showing the relationship of the parts as the stitch is beingset and new thread is being drawn from the thread supply.

FIG. 6 is similar to FIG. 5 but shows the relationship of the parts whenthe bobbin thread supply is exhausted.

Referring now to the drawings, the present invention is embodied in asewing machine having a bracket arm 10 terminating m a head 11 in whichthere is mounted a reciprocating needle bar 12 carrying at its lower enda needle 13. While the application of the present invention is notrestricted to any particular type of sewing machine the invention isincorporated for purposes of illustration in a cyclically operatedsewing machine, as for atom ' quires.

(hice example a buttonhole sewing machine, wherein the machine sews apredetermined number of stitches after which the buttonhole is slit. Tothis end, there is mounted in the head 11, a slitting knife 14 actuatedin the usual manner in timed sequence with the stitching cycle.

Also carried in the head 11 is the usual vertically movable take-up arm15 the outer end of which is provided with a thread eye 16. Secured tothe front of the head 11 is a face plate 17 on which is mounted a threadbreak sensing member 18 having an upper horizontal limb 19 extendingthrough a slot 20 formed in the face plate 17 and being located at apoint adjacent the topmost position of travel of the take-up arm 15, asshown in FIG. 1. Secured to the upper horizontal limb 19 is aninsulating sleeve 21 carrying on its inner side a contact 22 adapted toengage the take-up arm 15 in a manner hereinafter to be described.

Integral with and vertically depending from the upper horizontal limb 19(FIG. 2) is an upper vertical reach 23 disposed on the inside of theface plate 17 and journaled thereon by a pair of spaced bearing elements24 fastened to the face plate by screws 25. Secured on the uppervertical reach 23 are spaced collars 26 and 27 engageable with thebearing elements 24 such that vertical movement of the thread breaksensing member 18 is prevented. Depending from the upper vertical reach23 and connected thereto by a laterally and forwardly bent portion 28extending through a notch 29 in the face plate 17 is a lower verticalreach 30 having a lower horizontal limb or thread feeler finger 31extending in the opposite direction from the upper horizontal limb 19and lying in the path of movement of the needle thread 1 extendingbetween the take-up arm 15 and the needle 13. A forwardly bent threadretaining limb 31a retains the thread t within the confines of thethread feeler finger 31.

Normally urging the contact 22 toward the take-up arm 15 and into thepath of movement thereof is a spring 32 which encircles the upper reachsection 23 adjacent to the portion 28. One end of the spring 32 isanchored on the face plate by the screw 25 and the other end encirclesthe lower reach section 30. Limiting the movement of the upper limb 19toward the take-up arm '15 is a stop plate 34 fixed to the upper reach23 and adjustable in response to turning of screw 33.

Electrical leads 35 and 35a, leading respectively from the contact 22 tothe low voltage control unit 36 and from the control unit to the machineframe, form an open circuit which when closed by engagement of thecontact 22 and take-up 15 is effective to energize the control unit 36.The control unit may then transmit a visual or audible signal indicatingthat the thread has broken or the thread supply is exhausted. Thecontrol unit may also provide for automatic stopping of the machine.

The operation of the thread break sensing arrangement is as follows:

When the needle thread I is unbroken and stitches are being formed inthe conventional manner the needle thread travels from its source, overa guide member 37 through a thread tension 38, through the check springthrough the eye 16 of the take-up arm 15, across the face plate 17, intoa thread guiding slot 39 and thence through the eye of the needle 13.During normal stitch formation the take-up arm 15 travels in a verticalpath alternately giving and taking up thread as the stitch formation re-During this giving and taking up of thread the length of thread textending between the take-up arm 15 and the material being stitched istightened across the front surface of the face plate 17 only when thetake-up arm moves upwardly toward its top position where it exerts amaximum tension on the thread. Thus, when thread is eing given up thethread 1 merely slides or drops over the thread feeler finger 31 and thethread break sensing member 18 is urged clockwise, as viewed in FIGS. 3and 4, by the spring 32 and positions the contact 22 on the upper limb19 in the path of movement of the take-up arm 15. However, since thecontact 22 is located adjacent to the topmost position of the take-uparm 15 during the downward movement of the take-up arm 15 the contact 22will not be engaged during this period of stitch formation. As thetake-up moves upwardly, particularly as it approaches the top of thestroke, the needle thread 1 is being drawn tight and when substantiallyat the top of its stroke it draws the previously formed stitch tight.Accordingly, at this time, as shown in FIGS. 1 and 3, the thread I isdrawn upwardly in the thread guiding slot 39 and tightened across theouter surface of the face plate 17 whereupon the tightened thread tengages the thread feeler finger 31 adjacent the retaining limb 31a andis efiective to apply a turning movement on the thread sensing device 18to turn the limb i9 counterclockwise against the action of the spring 32and thereby prevent the contact 22 from engaging the take-up arm 15.

In the event that the needle thread t is broken, as shown in FIG. 4,this condition wiil be sensed by the thread feeler finger 31 since thethread merely drops slack and the thread break sensing member 18 is notturned. The contact 22 will then remain in its spring-urged position inthe path of the take-up arm 15 which, when the latter reaches itstopmost position, will engage the contact 22 and energize the controlunit 36.

In FIG. there is illustrated the relative positions of the take-up armand the contact 22 at stitch setting when the needle thread tis unbrokenand there is a supply of bobbin thread 12 on the usual bobbin housedwithin the loop taking member 49. It is to be observed that as thethreads t and b are being set to form the lock stitch in the work thebobbin thread b holds one end of the needle thread I fixed in the workwhereby the latter is held tight and in engagement with the threadfeeler finger 31,. Hence, as above described in connection with thesensing of a break in the needle thread 2, the tightening of the needlethread I applies a turning movement to the thread break sensing member18 to move the contact 22 out of engagement with the take-up arm 15.

As shown in FIG. 6, when the bobbin thread b is exhausted the needlethread 2 is slack, since the increment of needle thread t drawn from itssource during the feeding of the work in is no longer concatenated withthe bobbin thread b. It is readily apparent that in a slack conditionthe needle thread t is incapable of applying a turning movement to thethread break sensing member 13 for moving the contact 22 out of itsspring urged position and the latter will contact the take-up arm whenit reaches its topmost position as shown in FIG. 6.

Having thus set forth the nature of the invention, what we claim hereinis:

1. A device for use with a sewing machine for sensing a break in orexhaustion of the thread supply, comprising a. control device forindicating when said sewing thread supply is broken or exhausted, a pairof electrical contacts to complete a circuit to said control device whensaid thread supply is broken or exhausted, said pair of contacts meetingonly when said thread supply is broken or exhausted, a first of saidcontacts being normally urged into the plane of travel of said secondcontact, and means to urge first contact out of said plane of travel ofsaid second contact only during that portion of a sewing cycle when astitch is being set.

2. In combination with a sewing machine comprising a frame having stitchforming instrumentalities supported thereon and including a verticallymovable thread take-up device, an electrical control unit for indicatinga break in or exhaustion of the thread supply, switch means forenergizing said control unit when the thread supply is broken orexhausted, said switch means comprising two movable contacts, saidvertically movable take-up device comprising one of said contacts, saidswitch means being operable only when said take-up device is atsubstantially the high point of its vertical travel.

3. In combination with a sewing machine comprising a frame having stitchforming instrumentalities supported thereon and including a verticallymovable thread take-up device, an electrical control unit for indicatinga break in or exhaustion of the thread supply, switch means forenergizing said control unit when the thread supply is broken orexhausted, said switch means comprising two movable contacts, saidvertically movable thread take-up device comprising a first of saidcontacts, said second contact being normally biased into the path oftravel of said take-up device, and means operable when said threadsupply is unbroken to urge said second contact from the path of travelof said take-up lever as it approaches the high point of its verticalpath.

4. In combination with a sewing machine comprising a frame having stitchforming instrumentalities supported thereon and including a verticallymovable thread take-up device, an electrical control unit for indicatinga break in or exhaustion of the thread supply, switch means forenergizing said control unit, said switch means comprising two movablecontacts, said vertically movable thread take'up cor rprising a first ofsaid contacts, a vertically disposed thread break sensing membercarrying said second contact, said thread sensing member mounted forpivotal turning about its vertical axis; a spring normally biasing saidthread break sensing member about its vertical axis to bring said secondcontact carried thereby into the path of travel of said thread take-upmember, and means to urge said thread break sensing member about itsvertical axis in opposition to said spring when said thread supply isunbroken.

5. In combination with a sewing machine comprising a frame having stitchforming instrumentalities supported thereon and including a verticallymovable thread take-up device, an electrical control unit for indicatinga break in or exhaustion of the thread supply, switch means forenergizing said control unit, said switch means comprising two movablecontacts, said vertically movable thread take-up comprising a first ofsaid contacts, a vertically disposed thread sensing member carrying saidsecond contact, said thread sensing member mounted for pivotal turningabout its vertical axis, a spring normally biasing said thread sensingmember about its vertical axis to bring said second contact carriedthereby into the path of travel of said thread take-up member, and anarm integral with and extending laterally from said vertical threadsensing member in the path of the needle thread between the take-up andthe needle responsive to the tightening of the needle thread at thatpoint in the sewing cycle when the stitch is being set to urge saidthread break sensing member out of the path of travel of said take-upmember.

References Cited in the file of this patent UNITED STATES PATENTS1,042,602 Roberts et al Oct. 29, 1912 1,738,142 Gail Dec. 3, 19291,742,953 Gahlert et al. Jan. 7, 1930 2,400,529 Behrens May 21, 19462,868,151 Winz Jan. 13, 1959

